Such an arrangement is disclosed in U.K. patent specification No. 1,404,078, from which it is known to replace the mechanical interrupter contact present in a dial by an electronic interrupter contact. It is then important that the electronic interrupter contact closely approaches the properties of the mechanical interrupter contact.
It is of particular important that the value of the resistance of the contact is very large in the opened condition and very small in the closed condition.
The value of the resistance in the open as well as in the closed condition is determined not only by the choice of the element but also by the circuit into which the contact is incorporated.
Applicants found that with the line interruption arrangement known from the above-mentioned United Kingdom Patent Specification the problem is encountered that the voltage drop across the electronic interrupter contact is not sufficiently small for low line currents, such as those in very long subscriber's lines. A low voltage drop across the switching contact is a particular requirement for a long subscriber's line in order that the supply voltage to the remaining equipment is sufficient.
This undesired voltage drop is caused by the fact that the control energy of the electronic interrupter contact decreases in response to a decreasing line current causing the voltage drop across the contact increases.